This invention relates generally to air conditioning and heat pump systems and, more particularly, to a method and apparatus for optimizing the outdoor air flow for overall system efficiency and reliability.
In the design of air conditioning and heat pumps systems, it is common practice to use an outdoor fan motor equipped to operate at one or two speeds. As such, the design is performance and efficiency optimized at specific operating conditions. While performance at other operating conditions is not as efficient, it has generally been considered acceptable on the basis of system design economy.
One problem with such conventional design is that, while the design is economical in terms of first cost, the overall cost of the system, when including operating costs for its lifetime, are substantially increased by these operational characteristics. To elaborate, the speed and the corresponding power consumption of the outdoor fan motor is set at a relatively high level to meet the capacity and efficiency requirements of the system at extremes of outdoor temperature. Systems use the single speed motor to operate at this power consumption rate throughout the operating range even when the higher air flow is not required to meet the system needs. Specifically, at milder outdoor temperatures, for either heating or cooling, less air flow is required to perform the work required on the coil, than that required at the extreme temperatures. Similarly, on windy days when the volume of air flowing through the coil is increased by the wind itself, the fan tends to do more work then is necessary. On the other hand, if a condition should exist such that the effectiveness of the coil is diminished, such as a build up of dirt in the coil, or an obstruction in the inlet or discharge path of the air, then the point for which the system has been optimized will no longer be correct for normal optimized operating conditions.
It has long been recognized that there exists a temperature below which the air conditioning or heat pump system can not reliably be used as an air conditioner. Typically these applications involve the cooling of computer rooms where air conditioning may be required at outdoor temperatures down to 0.degree. F. As the lower temperatures are approached, the condensing temperature of the refrigerant in the condenser also drops, and this in turn produces a corresponding reduction in the head pressure on the high pressure side of the refrigeration system. This problem has been addressed by an associated reduction in fan speed in such a manner as described in U.S. Pat. No. 3,196,629 issued on Jul. 27, 1965 and assigned to the assignee of the present invention. It should be recognized that, while this technique does generally function to lower the fan speed with lower temperatures, it only operates in the lower ambient temperature conditions (e.g. below 55.degree. F.) and does little to improve the efficiency of the system. However, the requirements that bring about the use of such a system should be kept in mind when addressing the above problems relating to efficiency.
It is therefore the object of the present invention to provide an air conditioner with improved efficiency.
It is another object of the present invention to optimize the fan air flow delivery rate and motor power consumption over a full range of operation.
Yet another object of the present invention is the provision for optimizing the flow of air over the outdoor coil despite the occurrence of changes in ambient and system operating conditions.
Yet another object of the present invention is the provision for a motor control system that is economical to manufacture and efficient in use.
These objects and other future advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.